In many applications there is a requirement for inexpensive transparent conducting layers, but a busbar will be also required for some of the (large area) applications. Highly conductive (non-transparent) patterns can be made by screen-printing conducting pastes such as silver or carbon black pastes. Vacuum evaporation of metals through shadow masks is another method. Yet another method makes use of homogeneous conductive metallized surfaces which can be patterned by use of photoresist technology in combination with a metal etching agent. Photographic films can, under certain conditions, be used for making electrically conductive-silver “images”.
U.S. Pat. No. 3,664,837 describes the use of light sensitive evaporated silver halide film which upon exposure and after development results in conductive images. DE 1,938,373 describes a photographic method for producing conducting paths, resistances and capacitors for microcircuits starting from coated silver halide emulsions. U.S. Pat. No. 3,600,185 describes the production of electrically conductive patterns by means of diffusion transfer techniques.
DE-A 1938373 discloses a process for manufacturing passive elements such as resistances, capacitors, RC-components and conductive track by negative development with the aid of a light-sensitive multilayer silver halide material, comprising a non-conductive support and two different spectrally sensitized gelatin-containing silver chlorobromide emulsions one above another with a gelatin/silver ratio of at least 1:3, which are separated by a photographic bath permeable dielectric layer, which are developed in the presence of a known development booster.
Combinations of a transparent polymer-based conductor and a high conductive (non-transparent) pattern are described in some publications.
DE-A 196 27 071 discloses an electroluminescent configuration, which contains hole and/or electron injecting layers, wherein the polymeric organic conductor is selected from the group of polyfurans, polypyrroles, polyanilines, polythiophenes and polypyridines. DE-A 196 27 071 also discloses the use of poly(3,4-ethylenedioxythiophene) as a charge-injection layer on transparent metallic electrodes such as ITO (indium-tin oxide) and that the following materials are suitable as transparent and conductive materials: a) metal oxides e.g. ITO, tin oxide etc.; b) semi-transparent metal films e.g. Au, Pt, Ag, Cu etc. The latter being applied by vacuum techniques.
EP-A 510 541 discloses an organic electroluminescent device having an anode, an organic hole injection transport layer, an organic luminescent layer and a cathode formed sequentially in this order, wherein the organic hole injection transport layer contains a metal complex and/or a metal salt of an aromatic carboxylic acid. EP-A 510 541 further discloses that the conductive layers used in such devices may have a multi-layer structure by depositing different types of conductive materials selected from a metal, e.g. Al, Au, Ag, Ni, Pd or Te, a metal oxide, carbon black or a conductive resin such as poly(3-methylthiophene), but no specific combinations are exemplified.
U.S. Pat. No. 5,447,824 discloses a method of manufacturing a pattern of an electrically conductive polymer on a substrate surface, said method comprising: a) forming a liquid layer on a surface of said substrate from a solution containing a material capable of forming said electrically conductive polymer upon being heated, e.g. 3,4-ethylenedioxythiophene, an oxidizing agent and a base, b) exposing said liquid layer to patterned radiation, and c) heating said layer thereby forming a pattern of an electrically conductive polymer, said conductive polymer being formed in unexposed areas and a non-conductive polymer being formed in the exposed areas of the layer. The galvanic provision of the conductive polymer pattern with a metal layer, e.g. silver, copper, nickel or chromium, is also disclosed in U.S. Pat. No. 5,447,824.
WO 98/54767 discloses a conductive layer system, particularly for a transparent or semi-transparent electrode or electroluminescent configuration, comprising at least two layers, characterized in that the first layer contains an organic or organometallic electrically conductive polymer, which is transparent or semi-transparent in the visible range of the electromagnetic spectrum, e.g. a polymer selected from the group consisting of polythiophene, polypyrrole, polyaniline, polyacetylene or their optionally substituted derivatives and the second layer contains at least one electrically conductive inorganic compound or a metal or an appropriately doped semi-metal e.g. a material selected from the group consisting of Cu, Ag, Au, Pt, Pd, Fe, Cr, Sn, Al or their alloys or conductive carbon. In a preferred embodiment the second layer is a conductive pattern formed by an open grid structure, preferably with a 5–500 μm grid so that it cannot be perceived by the human eye. Invention example 2 discloses a poly(3,4-ethylenedioxythiophene)[PEDOT]/poly(styrene sulphonate)[PSS] layer with a surface resistivity of 1500 Ω/square to which conducting tracks of Leitsilber™ (a silver particle dispersion) ca. 2 mm wide had been applied by a printing technique.
The layer configuration disclosed in Example 2 of WO 98/54767 has the disadvantages of the grid of Leitsilber™ requiring a thickness of 5 to 10 μm to realize layers with a surface resistance of 0.5 to 1 Ω/square, which means that the surface of the configuration will have a certain roughness which will limit its applications, making it difficult to apply a thin, e.g. 100 nm, functional layer. Furthermore, an aqueous PEDOT/PSS dispersion would not wet such a Leitsilber™ grid and hence a usable multilayer conductive configuration would not result.
Furthermore, such a reversed order: first a conductive metal grid and then a conductive transparent polymeric layer will certainly be of more importance in LED devices and thin film photovoltaic devices, in which the transparent polymeric electrode performs as a hole-injecting layer.